1. Field of the Invention
The present invention relates to methods and apparatuses for forming a smooth surface and, more particularly, methods and apparatuses for forming a smooth laminate surface.
2. State of the Art
In recent years, workers in the battery art have begun to understand and recognize the advantages of so-called "laminate" batteries including solid polymer electrolytes and sheet-like anodes and cathodes. The advantages include lower battery weights than conventional batteries that employ liquid electrolytes, longer service life, relatively high power densities, relatively high specific energies, and the elimination of the danger associated with batteries containing spillable liquid electrolytes such as acids.
Laminate batteries using polymer electrolytes have been developed which possess good performance characteristics. For example, in U.S. Pat. No. 4,925,751, a laminate battery in which a cathode material formed from a mixture of an active cathodic material (preferably vanadium oxide V.sub.3 O.sub.8 or V.sub.6 O.sub.13), a conductive filler material (preferably carbon particles or filaments), and an ionically conductive polymer electrolyte material is laminated on a conductive substrate material such as a nickel or copper web or sheet. A layer of polymer electrolyte material is laminated over the laminated layer of cathode material, and an anode material is applied over the laminate layer of polymer electrolyte material. The cathode material is applied on the substrate by conventional coating techniques such as with a doctor blade method or an extrusion method.
The problems associated with production of laminate batteries include the viscosity of the cathode material, which is often as high as 1,000,000 centipoise. Because the cathode material is so viscous, it is generally necessary to form the cathode material layer by extruding the cathode material in the form of a bead or sheet onto the conductive web substrate, and then compress the cathode material between forming rollers that squeeze the cathode material to form the cathode material layer. Unfortunately, the cathode material tends to have a paste-like consistency and often sticks to the process equipment used in forming the cathode material layer, necessitating constant cleaning of the rollers and resulting in poor quality cathode material layers. Accordingly, it is desirable to provide a method and apparatus for forming a laminate having a smooth surface in which the tendency of material to adhere to process equipment used in forming the surface is minimized.